The present invention relates to a radar system for automotive vehicles, and more particularly, to a position detection system in a source vehicle for determining the relative position of a target.
Auto manufacturers are investigating radar, lidar, and vision-based pre-crash sensing systems to improve occupant safety. Current vehicles typically employ accelerometers that measure vehicle body decelerations in the event of a crash. In response to accelerometers, airbags or other safety devices are deployed.
In certain crash situations it would be desirable to provide information before forces actually act upon the vehicle when a collision is unavoidable. Such information may include the position of a target vehicle relative to a source vehicle.
Remote sensing systems using radar are used in adaptive cruise control, collision avoidance and collision warning applications. These systems have characteristic requirements for false detection. Generally, the remote sensing system reliability requirements for pre-crash sensing for automotive safety related systems are more stringent than those for comfort and convenience features, such as, adaptive cruise control. The reliability requirements even for safety related features vary significantly, depending upon the safety countermeasure under consideration. For example, tolerance towards undesirable activations may be higher for activating motorized belt pre-tensioners than for functions such as vehicle suspension height adjustments. Non-reversible safety countermeasures, including airbags, require extremely reliable sensing systems for pre-crash activation.
To meet wide-angle coverage requirements for pre-crash sensing purposes, multiple pulsed radar based sensing systems are being investigated for automotive applications. Multiple, pulsed radar sensor based systems with a wide field of coverage are available. Triangulation techniques with individual radar range measurements are used with multiple pulsed radar systems for object position estimation.
Triangulation techniques used for object position identification may result in the occurrence of false intersections or ghosts and inaccuracies in object bearing estimations due to individual radar sensor range measurement errors. Ghost elimination is an important aspect of object track initiations and track data associations, and various proprietary techniques are employed by radar tracking system developers for this task.
The accuracy with which range can be measured by a radar is limited by the signal bandwidth and signal to noise ratio. Many other error sources particular to individual radars also act to limit range measurement accuracy where inaccuracies cause large variations in object azimuth position estimation with triangulation techniques. Accurate azimuth position estimation is needed for reliable object tracking and threat assessment for automotive safety applications.
It would therefore be desirable to provide a reliable method for determining the position of a target vehicle.
The present invention provides an improved pre-crash sensing system that improves azimuth measurements and therefore provides more accurate angular position information for a target vehicle.
In one aspect of the invention, a sensing system for an automotive vehicle includes a first radar sensor and a second radar sensor generating a first range signal and a second range signal related to the target object, at two separate times. A controller is coupled to the first radar sensor and the second radar sensor. The controller calculates a first position and a second position from the first radar sensor and the second radar sensor range measurements. The controller generates a first set of points corresponding to the first position and a second set of points corresponding to the second position. The controller calculates a plurality of range-rate values in response to the first set of points and the second set of points. The controller compares the plurality of calculated range-rate values to the measured range-rate and selects the closest range-rate from the plurality of range-rate values. A couple of target position points are generated, one from the first set of points and the other from the second set of points that correspond to the closest measured range-rate.
In a further aspect of the invention, a method of determining the position of a target vehicle comprises: determining a first range and a second range from a first radar and a second radar sensor; calculating a first position and a second position from the first range and second range measurements; evaluating a measured range-rate; generating a first set of points corresponding to the first position; generating a second set of points corresponding to the second position; calculating a plurality of calculated range-rate values in response to the first set of points and the second set of points; comparing the plurality of calculated range-rate values to the measured range-rate; selecting the closest calculated range-rate from the plurality of calculated range-rate values to the measured range-rate; selecting a couple of target position points from the first set of points and the second set of points corresponding to the closest calculated range-rate to the measured range-rate.
One advantage of the invention is that by more accurately determining the relative position of the target vehicle, activation of the proper countermeasure at the proper time is more accurately performed.